1. Field of the Invention
The present invention relates, generally to a dual clutch transmission and, more specifically, to a dual clutch transmission with axially parallel clutches having an improved backing plate assembly.
2. Description of the Related Art
In the art of providing motive power to motor vehicles, power shifting transmissions have evolved as the latest approach to automatically transferring power from the prime mover, or engine, to the driven wheels. Power shifting transmissions can take the form of a dual, or twin, clutch transmission where the torque input from the engine is delivered to two input shafts each supporting a portion of the gear sets. Each input shaft has an associated clutch to selectively transfer torque provided by the engine. Since the input engine torque comes through a single input member, such as the flywheel or crankshaft, the two clutch assemblies are typically structured in a dual co-axial assembly having an axially parallel arrangement. The dual clutch assembly is operatively disposed about the two input shafts, which are also in a co-axial and co-centric arrangement.
To selectively engage and disengage their respective input shafts, the two clutches of the dual clutch transmission are each comprised of a set of clutch discs, also referred to as a clutch pack. The clutch packs each include one set of discs physically coupled to one of the input shafts and another set of discs physically coupled to the torque input member. The clutches are engaged by compressing the two sets of discs together against a fixed back plate. Conventional dual clutch art provides that the two clutch packs are juxtaposed to each other about a dual co-axial input shaft assembly so that when either of the clutch packs are compressed, they are pressed from either axial end against a common end or back plate that is disposed between them. The end plate is also referred to as a “backing plate.” The two sets of clutch discs in each clutch pack are alternately supported by inner and outer disc supports. To provide efficient construction of the dual clutch assembly, the two clutch packs have a common disc support that is operatively coupled to the torque input. The common disc support may be either the inner or the outer disc support depending upon the overall design. The disc supports may be shafts, bushings, or the like. Regardless, the backing plate is axially fixed to the common disc support to provide a solid immovable plate to compress the discs of each of the clutch pack against.
There are a number of conventional approaches to providing a backing plate between the two clutch packs. One known approach provides a common inner disc support that includes a radially extending flange, which is integral to the disc support and serves as a backing plate. This one-piece type of backing plate construction provides a common backing plate for each clutch pack, but is expensive to produce.
Other approaches to backing plate structure for dual clutch assemblies provide that the backing plate does not have to be integrally formed with the inner disc support, but can also be a separate piece or pieces that are rigidly connected to the inner disc support by axially fixing them to the inner disc support. For example, in an attempt to provide certain cost-effective solutions, some prior art approaches employ two backing plates that are fixed to the inner disc support with one or more snap rings. As shown in FIG. 2, one prior art approach shows a dual clutch assembly 50 with an axially parallel design with two backing plates 60 and 61 each fixed to an inner disc 55 support by snap rings 62 and 63, respectively. The snap rings 62, 63 attach each backing plate 60, 61 axially in one direction. The axial compressive forces that engage the right side clutch pack 52 are supported against both backing plates 60, 61. The axial compressive forces that engage the left clutch pack 51 are only supported by the left backing plate 60 against the right snap ring 63. The right backing plate 61 and the left snap ring 62 are unstressed in this case. In FIG. 3, another prior art approach shows a dual clutch assembly 70, similar to that shown in FIG. 2, wherein two backing plates 71 and 72 are supported against a single snap ring 73 disposed equally between the plates 71, 72.
While providing certain advantages over the solid flange backing plate construction previously mentioned, the prior art structure illustrated in FIGS. 2 and 3 also have disadvantages and drawbacks. The prior art backing plate approaches shown in FIGS. 2 and 3 require two separate backing plates, which must be mounted from both sides of the inner disc support and that have twice the mass and inertia of a single backing plate design. Thus, the two backing plate approach adds cost to the assembly process and adds inefficient parasitic losses from their weight.
Further, due to the prior art placement of the snap rings in either of these designs, the backing plates are not supported across their base surface at the inner disc support resulting in relatively low rigidity. Thus, in the prior art, when either clutch pack in engaged, the respective backing plate deforms radially and presses against the opposing backing plate. This radial deformation of the backing plates cause the clutch discs, which lie close to the backing plates, to wear very unevenly. Resulting in inaccuracy and inefficiency in the engagement of the clutches, poor clutch and transmission performance, and early failure of the clutch packs.
Accordingly, there remains a need in the related art for a backing plate assembly for an axially parallel dual clutch arrangement that is cost efficient to manufacture, simple to install, and has a high rigidity.